Medial collateral ligament (MCL) injury is the most common ligamentous injury of the knee. Such injuries frequently cause pain and joint instability and may subsequently disable affected persons for several weeks to months. Research on the natural course of MCL healing has determined that structural and biochemical properties remain-inferior to uninjured MCLs for up to 2 years, perhaps indefinitely. Low-intensity therapeutic ultrasound (US) has been found to improve healing of both skin and tendon injuries. There are no studies in which the effects of US on ligament healing have been examined. The objective of this project is to examine the effectiveness of US on Improving healing of the MCL following injury. Using a rabbit model in which the MCL has been surgically transected, healing will be evaluated by determining the material properties via mechanical testing, total collagen content, total cellularity, and the ratio of type I versus type III collagen. Three questions will be addressed: l. Is there a statistically significant difference in biomechanical and biochemical properties of healings MCLs treated with US compared to sham-treated controls in the early phases of healing? 2. Are these differences maintained over time? 3. Does treatment with US for 4 weeks result in improved healing when compared to treatment for two weeks?